Radio frequency switch

ABSTRACT

A radio frequency switch is disclosed. The RF switch uses a combination of transistor technology and a topology to create an RF switch that has a high isolation and a high voltage breakdown at frequencies including those above a gigahertz.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/844,878, filed on May 8, 2019, the entire contents ofwhich is incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to radio frequency (RF) devices and morespecifically to an RF switch that can be used in RF tuning applications.

BACKGROUND

An RF switch is an important component for a front end portion of awireless system, such as a handset or a base station. In particular, anRF switch may be used for impedance (i.e. feed point) tuning (i.e.,matching) for maximum power transfer between a power amplifier and anantenna. Additionally, RF switches may be used for aperture tuning(i.e., matching) for maximum power transfer between an antenna and itsoperating environment. For example, multiple RF switches can be activelycontrolled ON/OFF to couple/decouple a variety of impedance combinationsinto a front end to optimize front end performance in response tochanging operating conditions.

Many wireless applications require RF switches to be physically small,to handle high powers, and to have low power dissipation (i.e., loss).Accordingly, low insertion loss, high isolation, and high breakdownvoltage are important requirements for an RF switch. Meeting all ofthese requirements, however, may be difficult, especially as wirelesssystems move to higher frequencies. A need, therefore, exists for new RFswitch circuits and methods to meet the requirements of wirelesssystems, especially at high frequencies.

SUMMARY

In at least one aspect, the present disclosure describes a radiofrequency (RF) switch. The RF switch includes a first III-V transistorthat is coupled between an input of the RF switch and a shunt-connectionnode. The first III-V transistor is controllable by a first controlsignal that is applied to a gate of the first III-V transistor. The RFswitch also includes a second III-V transistor that is coupled betweenthe shunt-connection node and an output of the RF switch. The secondIII-V transistor is controllable by the first control signal applied toa gate of the second III-V transistor. The RF switch also includes atleast one silicon-on-insulator (SOI) transistor that is coupled betweenthe shunt-connection node and a ground. The at least one SOI transistoris controllable by a second control signal that is applied to a gate ofthe SOI transistor.

In various implementations the III-V transistor can be gallium arsenide(GaAs), silicon carbide (SiC), or gallium nitride (GaN).

In another aspect, the present disclosure describes an RF tuning system.The RF tuning system includes an RF switch that is configured to switchan input to one of a plurality of outputs. For each output the RF switchincludes a pair of III-V switches and an SOI switch. The III-V switchesare connected in series between the input and the output and areconnected to each other at a shunt-connection node. The SOI switch isconnected between the shunt-connection node and a ground.

In an implementation the RF tuning system, the SOI switch is a stack ofSOI transistors (i.e., a plurality of series connected SOI transistors).

In another aspect, the present disclosure describes a method forswitching an RF signal. The method includes applying an RF signal to aninput node of an RF switch that includes two III-V switches connected inseries between the input node and an output node. The two III-V switchesare connected to each other at a shunt-connection node and a SOI switchis connected between the shunt-connection node and a ground. The methodincludes blocking the RF signal by controlling the two III-V switches tobe in an OFF condition to block all but a leakage portion of the RFsignal from the shunt-connection node and controlling the SOI switch tobe in an ON condition to short the leakage portion of the RF signal tothe ground. Alternatively, the method includes passing the RF signal bycontrolling the two III-V switches to be in an ON condition to pass theRF signal from the input node to the output node and controlling the SOIswitch to be in an OFF condition to decouple the ground from theshunt-connection node.

The foregoing illustrative summary, as well as other exemplaryobjectives and/or advantages of the disclosure, and the manner in whichthe same are accomplished, are further explained within the followingdetailed description and its accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a wireless system including an impedance(feed point) turner according to a possible implementation of thepresent disclosure.

FIG. 2 is a block diagram of a wireless system including an apertureturner according to a possible implementation of the present disclosure.

FIG. 3 is a schematic of a front end subsystem for a wireless systemaccording to an implementation of the present disclosure

FIG. 4 is a schematic of multi switch tuner according suitable for usein a RF front end according to an implementation of the presentdisclosure.

FIG. 5A is a functional diagram of an RF switch in an ON condition.

FIG. 5B is a functional diagram of an RF switch in an OFF condition.

FIG. 6A is a schematic of a transistor forming a switch according to animplementation of the present disclosure.

FIG. 6B is a schematic of a stack of series connected transistorsforming a switch with a higher break down voltage than the switch ofFIG. 6A according to an implementation of the present disclosure.

FIG. 7 is a schematic of an RF switch according to a first possibleimplementation of the present disclosure.

FIG. 8 is a schematic of an RF switch according to a second possibleimplementation of the present disclosure.

FIG. 9 is a flowchart of a method for switching RF according to animplementation of the present disclosure.

The components in the drawings are not necessarily to scale relative toeach other. Like reference numerals designate corresponding partsthroughout the several views.

DETAILED DESCRIPTION

The present disclosure describes an RF switch that has a high isolation,a low insertion loss, and a high breakdown voltage over a wide range offrequencies. In a non-limiting example, the disclosed RF switch mayoperate over a frequency range of about 500 megahertz (MHz) to 10gigahertz (GHz) with an isolation of greater than 10 decibels (dB)(i.e., a high isolation), an insertion loss of less than 0.4 dB (i.e., alow insertion loss), and a breakdown voltage level of more than 70 volts(i.e. a high breakdown voltage). This performance is made possible theuse of a combination of technologies configured in a circuit topologythat uses strengths of each technology while mitigating weaknesses ofeach technology.

The disclosed RF switch uses a topology and a combination of switchtechnologies (i.e., materials) to provide a performance (e.g., insertionloss, voltage breakdown, and isolation) suitable for RF tuningapplications. The topology includes two series connected transistorsthat couple the input of the RF switch to the output of the RF switchwhen the RF switch is in an ON condition. The two series connectedtransistors are a first material (e.g., GaN) and are connected togetherat a shunt-connection node. The first material switches cam provide asufficiently low insertion loss (i.e., when ON) but may have a lowerisolation (i.e., when OFF) than required by the application.Accordingly, the topology includes one or more transistors coupledbetween the shunt-connection node and a ground. The one or moretransistors can be configured (i.e., turned ON) when the seriestransistors are OFF to increase the isolation of the RF switch byshorting any leakage signals to ground. The one or more transistorsutilize a second material (e.g., SOI or CMOS) that can provide anisolation (i.e., when OFF) sufficiently large so that the low insertionloss of the two series connected transistors (i.e., when ON) is notsignificantly reduced. Further, the number of the one or moretransistors may be selected based on a desired breakdown voltage. Thus,the disclosed RF switch uses the strengths of topology and materialtechnology to provide an RF switch with desirable operating properties(e.g., at high RF frequencies and at high powers).

The RF switch of the disclosure may be used in an RF front end subsystemof a wireless system, such as a base station of a cellular network or ahandset of a cellular network. In these applications, the RF switch maybe used at frequencies of, for example, 900 MHz or 2.6 GHz. The RFswitch may be configured to perform a function as part RF tuning system.To help understanding, the disclosed RF switch will be described inthese terms. The RF switch of the disclosure is not limited, however, tothese particular implementations.

FIG. 1 is a block diagram of front end subsystem (i.e., front end) for awireless system that includes an impedance tuner (i.e., feedpointtuner). The front end includes an RF power amplifier 110 coupled to anantenna 130 through the impedance tuner 120. The impedance tuner 120compensates for fluctuations of the input impedance of the antenna, forexample, as a result of a changing operating environment. To minimize RFreflections (i.e., standing waves) in certain operating environments,the feedpoint impedance of the antenna is substantially matched to theoutput impedance of the RF power amplifier (e.g., 50 ohms). Not only canthis result in optimum (i.e., maximum) power transfer from the PA to theantenna, but also minimizes the risk of damage from a high voltagecreated by reflections from a highly mismatched antenna. The impedancetuner typically includes impedance elements that may be coupled ordecoupled to the RF circuit (i.e., switched IN/OUT of the RF circuit)until the reflections from the antenna are minimized.

FIG. 2 is a block diagram of a front end for a wireless system thatincludes an aperture tuner 140. The aperture tuner 140 compensates forfluctuations in a radiation efficiency of the antenna, for example, as aresult of a changing operating environment (e.g., change in operatingfrequency). The aperture tuner 140 typically includes impedance elementsthat may be coupled/decoupled to/from the antenna to adjust a parameterof the antenna (e.g., an effective length). In some implementations,both an impedance tuner and an aperture tuner may be used to ensure goodperformance (e.g., as measured by a parameter compared to a threshold)of the front end for a variety of operating environments (e.g., range ofoperating frequencies).

FIG. 3 is a schematic of an embodiment of a front end with an RF tuningsystem that includes an aperture turner 310 and an impedance tuner 320.The aperture tuner 310 and the impedance tuner 320 each include asingle-pole-four-throw (SP4T) RF switch that can be configured to couplefour different impedances to the front end circuit. The impedances mayinclude an open, a short, a capacitance (e.g., a variable capacitance),or an inductance (e.g., a variable inductance). While four throws areshown for the implementation illustrated in FIG. 3, any number ofterminals may be implemented. In operation, a sensing and control system(not shown) can sense a parameter of the RF circuit (e.g. a voltagestanding wave ratio (VSWR)) and adjust the switch to change (e.g., tominimize) the sensed parameter.

The RF switch for an RF tuning system may also be implemented as a bank(i.e., array) of single-pole-single-throw (SPST) switches. FIG. 4 showsa possible implementation of an RF tuning system 400 having a bank(i.e., a plurality) of RF switches 410 each coupled to a one of aplurality of outputs, with each output coupled to a different impedance(i.e., Z₁, Z₂, Z₃, Z₄), such as those described for FIG. 3. Each switchin the bank of RF switches 410 may be controlled to be in an ONcondition (i.e., shorted, closed, ON, etc.) or to be in an OFF condition(i.e., opened, OFF, etc.). For tuning, the RF switches may be controlledindependently to couple some combination (e.g., parallel coupledcombination) of impedances (i.e., Z₁, Z₂, Z₃, Z₄) to an input terminal420. The input terminal (i.e., node) may be coupled to an RF front endas in FIG. 3 to operate as an impedance tuner or as an aperture turner.

As discussed, the SPST implementation of the RF switch can form thebasis of a RF tuning system. The performance of the RF switch in asystem (e.g., the RF tuning system) can be described by its ability tocouple an RF signal in an ON condition (i.e., an ON state). FIG. 5Ashows the RF switch in an ON condition. In this condition, an RF signalis coupled (e.g., capacitively coupled between an input node (i.e.,input, input terminal) and an output node (i.e., output, outputterminal). The RF signal ideally loses no power to the RF switch as itis coupled between the input and the output (or vice versa). Practicallyhowever, the RF switch may have some insertion loss (IL), which mayplace constraints on the RF switch. For example, an RF switch with aninsertion loss of −0.5 dB dissipates more than a 1 W of power whenconducting a 10 W RF signal. The dissipation of this amount of powerplaces additionally requirements (e.g., size requirements) on the RFswitch, which can limit its used in certain applications (e.g., mobileapplications). Thus, it can be desirable to minimize IL, especially inhigh power RF applications, such as described previously. Additionally,having a low IL across a broad RF spectrum (i.e., wide bandwidth) offersadvantages because the RF switch can operate in either large bandwidthor low bandwidth applications (e.g., without a resonant matchingnetwork).

The performance of the RF switch in a system (e.g., the RF tuningsystem) can also be described by its ability to block an RF signal in anOFF condition (i.e., an OFF state). FIG. 5B illustrates animplementation of an RF switch in an OFF condition. Ideally in thiscondition, no RF signal is coupled between the input and the output (orvice versa). In other words, the ideal RF switch in the OFF conditionisolates the input and the output completely (i.e., infinitely highisolation). In practice, however, some amount of RF signal can leak fromthe input to the output (or vice versa). RF leakage can negativelyimpact an RF tuning system because the decoupling (e.g., of a tuningimpedance) is not complete when an RF switch is placed in an OFFcondition. As a result, the RF tuning system may not behave as designed.Thus, it can be desirable to maximize isolation (ISO) of an RF switchfor applications, such as described previously.

Some additional performance parameter of an RF switch in a system (e.g.,the RF tuning system) may be related to isolation. One such performanceparameter is voltage hold off (i.e., voltage breakdown). A voltageapplied to the RF switch may be sufficient to breakdown the highimpedance provided by the switch in the OFF condition. It can bedesirable to maximize the ability of the RF switch to hold off thesehigh voltages. For example, an RF switch may need to withstand high RFvoltages (e.g., >60-70 V) reflected by an impedance miss-matched (non 50ohm) antenna driven at full power. In another example, an RF tuningsystem (e.g., as described previously), may experience high voltages asa results of a large voltage standing wave ratio (VSWR) created duringoperation (e.g., while impedances are switched to determine a match).For proper operation in such systems, it is desirable that an RF switchhas a high break down voltage (V_(BD)) to survive such events.

Another performance parameter of an RF switch is linearity. Thelinearity of an RF switch can affect the output signal in a variety ofways. In an ON condition, the RF switch can couple an RF signal from aninput to an output via some impedance (e.g., capacitance). The RF signalmay include multiple frequencies over a bandwidth. In an idealimplementation, all constituent frequencies of the RF signal are coupledlinearly from the input to the output of the switch. In practice,however, the coupling to the RF switch may not be linear so that theoutput RF signal is not a precise replica of the input RF signal. Inother words, the output RF signal is distorted. The distortions mayappear in the frequencies of the output signal as multiples (i.e.,orders) of a fundamental frequency. The (higher) orders (IIP2, IIP3) maybe compared to the fundamental as the RF signal power is changed todetermine the linearity of the switch. Additionally, a power curve ofthe RF switch may be analyzed to determine a power at which the RFsignal at the output is reduced from the RF signal at the input due topower nonlinearity (e.g., 0.1 dB compression point). It may be desirablethat the RF switch behaves linearly for all frequencies and powers. Theinsertion loss of the RF switch in the ON condition may, in someconditions, be used to identify a nonlinearity because it may correspondto power lost from a fundamental frequency. Thus, an RF switch with alow insertion may be desirable from a linearity standpoint.

A SPST RF switch can be implemented as a transistor. FIG. 6A is atransistor implemented as a SPST RF switch. In this implementation, afield effect transistor may be controlled ON/OFF by a voltage applied toa gate terminal 610 of the transistor to pass/block an RF signal appliedto an input terminal 620 (e.g., source terminal) to/from an outputterminal 630 (e.g., drain terminal). The voltage corresponding to theON/OFF condition of the transistor is based on the type (e.g., P-type,N-type) of transistor. The RF switch may be implemented as a P-type orN-type transistor. In one possible implementation, when a first voltageis applied to a gate terminal of the transistor, the transistor isconfigured into an ON condition, in which a low impedance (approximatelya short) path exists between the input terminal 620 and the outputterminal 630 of the transistor. When a second voltage is applied to thegate terminal of the transistor, the transistor is configured into anOFF condition, in which a high impedance (e.g., approximately an open)path exists between the input terminal 620 and the output terminal 630of the transistor.

Transistors can be fabricated from materials from group IV (4) of theperiodic table (e.g., Si, Ge). For example, silicon (Si) may be used asthe basis of a complementary metal oxide field effect transistor (i.e.,CMOS transistor). A CMOS transistor may have a low V_(BD), which can beraised by using a stack of series connected transistors, as shown inFIG. 6B. As shown, the stack includes adjacent transistors are connectedin series between an input terminal 620 and an output terminal 630. Thetransistors may be controlled simultaneously ON or OFF by applying thesame signal to a gate of each transistor in the stack. A voltageappearing across the stack is divided between the transistors in thestack so that a particular transistor of the stack receives a reduced(i.e., series divided) voltage. For example, the switch including astack of transistors (FIG. 6B) increases V_(BD) by a factor of six(i.e., the count of transistors in the stack) as compared to the RFswitch including a single transistor (FIG. 6A).

An insertion loss for a stack of transistors is proportional to a number(i.e., a count) of transistors in the stack. Accordingly, while using astack series connected transistors can increase V_(BD), it may increasean overall insertion loss. The performance (e.g., insertion loss) of aCMOS switch may be further degraded as the RF frequency is raised. As aresult, CMOS transistors are typically used at lower frequencies (e.g.,less than about 1 GHz).

The performance of a silicon (Si) based transistor at higher frequenciesmay be improved by the choice of transistor technology.Silicon-on-insulator (SOI) is a transistor architecture (i.e.,technology) Compared to a CMOS switch, an RF switch implemented as anSOI transistor may have less insertion loss and more isolation than aCMOS transistor at frequencies above 1 GHz (e.g., in a range of 1 GHz to3 GHz). Additionally, SOI transistors may have a smaller size (i.e.,than a comparable CMOS) and a more power handling capability (e.g. 1 W).For at least these reasons, an RF switch may be implemented as a SOItransistor in some mobile applications (e.g., cellular handset).

RF switches (i.e., switches, switching devices) may also be implementedas transistors fabricated from a compound containing elements from groupIII (3) and group V (5) of the periodic table. Switching devices madefrom these materials are known generally as “III-V” switching devices.When the switching device is a transistor, it may be referred to as a“III-V” transistor. The precise choice of III-V materials may be basedon a variety of requirements including (but not limited to) operatingfrequency and operating power. Some possible III-V transistors that maybe used in implementations of the present disclosure may include (butare not limited to) gallium arsenide (GaAs), silicon carbide (SiC) andgallium nitride (GaN).

While SOI offers a higher V_(BD) than CMOS, a (lossy) stack of SOItransistors may still be needed to hold off voltages associated withtuning applications. An RF switch using III-V material transistors canhold off a voltage associated with a tuning application using a stackwith fewer transistors than an equivalent RF switch using SOItransistors. GaN transistors have excellent (e.g., high) V_(BD)properties but can have poor (e.g., low) isolation due to a largecapacitance between a source terminal and a drain terminal in an OFFcondition. In other words, RF signals can be coupled through thecapacitance resulting in a low isolation GaN switch. The SOI switch mayhave a higher isolation than the GaN switch but may have a lower V_(BD)than t the GaN switch. In other words, a GaN switch may have arelatively high voltage breakdown but a relatively low isolation, whilea SOI switch may have a relatively high isolation (e.g., in a stackedconfiguration) but a relatively low voltage breakdown. The disclosed RFswitch uses a particular topology and combination of switch technologies(i.e., materials) to provide a voltage breakdown and an isolationsuitable for RF tuning applications.

An RF switch according to a possible implementation of the presentdisclosure is shown in FIG. 7. The RF switch 700 is coupled to a sourceat an input node (i.e., input) 701 and coupled to a load at an outputnode (i.e., output) 702. A first III-V switch 710 (e.g., a first GaNtransistor) is coupled between the input 701 (e.g., at a sourceterminal) and a shunt-connection node 720 (e.g., at a drain terminal). Asecond III-V switch 730 (e.g., a second GaN transistor) is coupledbetween the shunt-connection node 720 (e.g., at a source terminal) andthe output node (i.e., output) 702 (e.g., at a drain terminal). Thefirst III-V switch and the second III-V switch are controlled to havethe same ON/OFF state with a first control signal (i.e., first signal)760 applied to a gate of each switch. The ON state of each switch maycorrespond to a voltage of the signal above a threshold and the OFFstate may correspond to a voltage of the first signal 760 below athreshold, or vice versa.

The RF switch 700 also includes an SOI switch 740 that is coupledbetween the shunt-connection node 720 and a ground node (i.e., ground)703. The ON/OFF state of the SOI switch 740 is controlled with a secondcontrol signal (i.e., second signal) 770 applied to the gate of the SOIswitch 740. The second signal 770 and the first signal 760 can becomplementary ON/OFF signals. The ON/OFF state of the SOI switch isopposite to the states of the first III-V switch 710 and the secondIII-V switch 730.

The RF switch 700 may be turned ON to conduct an RF signal between theinput 701 and the output 702 by configuring the first III-V switch 710and the second III-V switch 730 in an ON state and the SOI switch in anOFF state. The SOI technology has excellent isolation in the OFF state.As a result, there can be very little leakage of the RF signal to groundso the overall insertion loss of the switch remains low.

The RF switch 700 may be turned OFF to block an RF signal between theinput 701 and the output 702 by configuring the first III-V switch 70and the second III-V switch 730 in the OFF state and the SOI switch inthe ON state. As mentioned, in the OFF state, III-V switches may haveleakage. For example, a leakage portion of an RF signal applied to theinput 701 may leak through the source-drain capacitance of the firstIII-V switch. In this scenario, the SOI switch in the ON state shortsthe leakage portion to ground. As a result, the isolation of the RFswitch 700 is increased.

As mentioned, a III-V switch has a high V_(BD). The V_(BD) is made evenhigher through the series stack formed by the first III-V switch 710 andthe second III-V switch 730. The SOI switch has a lower V_(BD) but theSOI switch is partially shielded from the voltage appearing at the input(or output) of the RF switch. For example, if the first III-V switch 710is broken down there is a voltage drop between the source and the drainof the first III-V switch that reduces voltage appearing at theshunt-connection node 720. Thus, the breakdown voltage requirement ofthe SOI switch 740 can be reduced.

An RF switch according to another possible implementation of the presentdisclosure is shown in FIG. 8. The SOI switch of the RF switch 700 isimplemented as a stack of SOI switches 740 in order to improve thebreakdown voltage of the SOI switch. As described above, if the firstIII-V switch 710 is broken down, then a voltage corresponding to thebreak down voltage of the first III-V switch appears at theshunt-connection node 720. Accordingly, the number of SOI transistor inthe stack of SOI transistor can be selected to hold off this voltage. Inother words, the number of SOI transistors in the stack may be based on(i.e., corresponding to) a breakdown voltage of one of the pair of III-Vswitches. In operation, the stack of the SOI switches are controlled toall be in an ON condition when the RF switch OFF and when the RF switchis ON, the stack of the SOI switches are control to all be in an OFFcondition.

FIG. 9 is a flowchart of a method for switching RF according to animplementation of the present disclosure. The method includes providing910 an RF switch having two III-V switches connected in series betweenan input node and an output node. The III-V switches may be implementedas GaN transistors. The transistors are connected to each other at ashunt-connection node. The RF switch also includes an SOI switchconnected between the shunt-connection node and a ground so that whenthe SOI switch is turned ON, RF signals at the shunt-connection node(e.g., via leakage) are grounded instead of appearing at the output nodeof the RF switch. The method also includes applying 930 an RF signal tothe input of the RF switch The method includes blocking 940 an RF signalby turning the III-V switches OFF and the SOI switch ON or passing 950the RF signal by turning the III-V switches ON and the SOI switch OFF.

Through the combination of transistor technologies (e.g., SOI, GaN) andthe stacked and shunted topology, the RF switch of the disclosure canoffer a high break down voltage and a high isolation for wide range offrequencies. For example, the RF switch may operate over a range fromabout 0.5 GHz to about 10 GHz with excellent performance. The RF switchmay operate at even high frequencies (e.g., up to 20 GHz) if performancerequirements are less critical.

In the specification and/or figures, typical embodiments have beendisclosed. The present disclosure is not limited to such exemplaryembodiments. The use of the term “and/or” includes any and allcombinations of one or more of the associated listed items. The figuresare schematic representations and so are not necessarily drawn to scale.Unless otherwise noted, specific terms have been used in a generic anddescriptive sense and not for purposes of limitation.

Some implementations may be implemented using various semiconductorprocessing and/or packaging techniques. Some implementations may beimplemented using various types of semiconductor processing techniquesassociated with semiconductor substrates including, but not limited to,for example, Silicon (Si), Gallium Arsenide (GaAs), Gallium Nitride(GaN), Silicon Carbide (SiC) and/or so forth.

While certain features of the described implementations have beenillustrated as described herein, many modifications, substitutions,changes, and equivalents will now occur to those skilled in the art. Itis, therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the scope of theimplementations. It should be understood that they have been presentedby way of example only, not limitation, and various changes in form anddetails may be made. Any portion of the apparatus and/or methodsdescribed herein may be combined in any combination, except mutuallyexclusive combinations. The implementations described herein can includevarious combinations and/or sub-combinations of the functions,components, and/or features of the different implementations described.

The invention claimed is:
 1. A radio frequency (RF) switch comprising: a first III-V transistor coupled between an input of the RF switch and a shunt-connection node, the first III-V transistor controllable by a first control signal applied to a gate of the first III-V transistor; a second III-V transistor coupled between the shunt-connection node and an output of the RF switch, the second III-V transistor controllable by the first control signal applied to a gate of the second III-V transistor; and at least one silicon on insulator (SOI) transistor coupled between the shunt-connection node and a ground, the at least one SOI transistor controllable by a second control signal applied to a gate of the at least one SOI transistor.
 2. The RF switch according to claim 1, wherein the first III-V transistor and the second III-V transistor are gallium arsenide (GaAs).
 3. The RF switch according to claim 1, wherein the first III-V transistor and the second III-V transistor are silicon carbide (SiC).
 4. The RF switch according to claim 1, wherein the first III-V transistor and the second III-V transistor are gallium nitride (GaN).
 5. The RF switch according to claim 1, wherein the first control signal and the second control signal are complementary ON/OFF signals that control the RF switch in an ON state or an OFF state.
 6. The RF switch according to claim 5, wherein in the ON state the first III-V transistor and the second III-V transistor are ON to create a low impedance path between the input and the output of the RF switch; and the at least one SOI transistor is OFF to isolate ground from the low impedance path.
 7. The RF switch according to claim 5, wherein in the OFF state the first III-V transistor and the second III-V transistor are OFF to create a high impedance path between the input and the output; and the at least one SOI transistor is ON to short the high impedance path to ground.
 8. The RF switch according to claim 1, wherein a breakdown voltage of the first III-V transistor and the second III-V transistor is higher than a breakdown voltage of the at least one SOI transistor.
 9. The RF switch according to claim 8, wherein the at least one SOI transistor is coupled to a voltage that is lower than a voltage coupled to first III-V transistor or the second III-V transistor.
 10. The RF switch according to claim 1, wherein the at least one SOI transistor is a stack of SOI transistors connected in series.
 11. The RF switch according to claim 10, wherein a number of SOI transistors in the stack corresponds to a break down voltage of the first III-V transistor or the second III-V transistor.
 12. The RF switch according to claim 1, wherein a frequency of an input signal to the RF switch is in a range between and including 0.5 gigahertz and 10 GHz.
 13. An RF tuning system comprising: an RF switch configured to switch an input to one of a plurality of outputs, and for each output the RF switch includes: a pair of III-V switches connected in series between the input and the output, the pair of III-V switches connected to each other at a shunt-connection node; and an SOI switch connected between the shunt-connection node and a ground.
 14. The RF tuning system according to claim 13, wherein the pair of III-V switches include; a first GaN transistor coupled between the input and the shunt-connection node; and a second GaN transistor coupled between the shunt-connection node and the output.
 15. The RF tuning system according to claim 13, wherein the SOI switch is a stack of SOI transistors.
 16. The RF tuning system according to claim 15, wherein a count of SOI transistors in the stack of SOI transistors corresponds to a breakdown voltage of one of the pair of III-V switches.
 17. The RF tuning system according to claim 13, wherein the RF switch is configured to switch the input to a particular output when the pair of III-V switches corresponding to the particular output are in an ON condition and the SOI switch corresponding to the particular output is in an OFF condition.
 18. The RF tuning system according to claim 13, wherein the RF switch is configured to isolate the input from a particular output when the pair of III-V switches corresponding to the particular output are in an OFF condition and the SOI switch corresponding to the particular output is in an ON condition.
 19. A method for switching an RF signal, the method comprising: applying an RF signal to an input node of an RF switch that includes two III-V switches connected in series between the input node and an output node, the two III-V switches connected to each other at a shunt-connection node; and blocking the RF signal by: controlling the two III-V switches to be in an OFF condition to block all but a leakage portion of the RF signal from the shunt-connection node, and controlling an SOI switch that is coupled between the shunt-connection node and a ground to be in an ON condition to short the leakage portion of the RF signal to the ground.
 20. The method for switching an RF signal according to claim 19, further comprising: passing the RF signal by: controlling the two III-V switches to be in the ON condition to pass the RF signal from the input node to the output node, and controlling the SOI switch to be in the OFF condition to decouple ground from the shunt-connection node. 